We hope to determine whether any clinical characteristics of patients with acute psychoses will predict the likelihood of a therapeutic response to lithium as opposed to neuroleptic treatment. Newly hospitalized psychotic patients, including manics, schizophrenics, and "schizoaffectives," are randomly assigned to lithium carbonate or chlorpromazine for a three-week double-blind trial. Although the series is not complete, we can report the following: (1) Diagnosis of mania or manic syndrome using checklist criteria (such as Research Diagnostic Criteria (RDC) or DSM-III) is more likely when data from family informants is used. (2) A positive therapeutic response to lithium is not less likely with a diagnosis (RDC) of "schizoaffective, manic" as opposed to "manic." Thus, the "schizophrenic" symptoms (delusions, hallucinations) used to differentiate these groups are not of much predictive value for drug response. (3) Schizophrenic patients without affective symptoms differ from schizoaffectives in (a) tending to respond less often to lithium or chlorpromazine and (b) having more normal simple reaction time.